The invention relates to building construction and, in particular, to a panel for use in constructing moistureproof back-up wall in three wythe perimeter wall construction and the wall provided thereby.
There is presently employed a type of three layer (withe) wall construction in low to mid-rise building (about 10 floors or less) in which a brick, concrete or other water permeable masonry exterior wall is backed up with steel stud mounted drywall covered with a moistureproof barrier. Moistureproof is used to refer to both waterproof and water vaporproof. An interior drywall layer forms the third withe of the construction. The masonry of the exterior wall is typically held to the building by ties extending from the vertical stringers through the drywall backup.
The conventional construction of such moistureproof back-up walls is the erection of a steel frame by mounting U-shaped galvanized steel channels to the facing upper and lower slab surfaces with power driven steel fasteners, mounting galvanized steel studs at regular intervals (typically 16 inches on center) between the floor and ceiling channel members with galvanized sheet metal steel screws and hanging conventional gypsum board panels adjoining one another to the studs by means of galvanized screws or other steel fasteners. The installed gypsum board panels are then typically "damp-proof" by a roofing or damp-proofing mechanic who either attaches a treated felt paper or trowls a damp-proofing mastic material over the exterior facing major planar surfaces of the panels and the joints between the panels. Mastic is perceived to be a more effective moisture barrier although a more expensive treatment than felt paper which is easily torn in mounting and which can separate from the gypsum panels. Masons then follow to install the outermost moisture permeable masonry wall, often puncturing the felt paper or mastic and underlying drywall to install wall ties. A conventional drywall is hung on the interior side of the studs to provide the third wythe.
A significant problem with this type of drywall-back-up construction is the high labor costs, particularly that associated with the application of the "damp-proofing". The mechanics are generally paid a craftsmen wage and the "damp-proofing" must be applied by hand to the entire surface of the installed back-up wall.
Yet another problem associated with the hand applied mastic type damp-proofing systems as currently installed is that no provision is made for eventual deterioration of the mastic between abutting drywall panels. Typically, the mastic is applied as quickly as possible with no special treatment being given to the seams between the adjoining gypsum board panels. The mastic is simply trowelled across the panels and over seams between the panels.
Another problem is that the thickness of the hand applied coating is never uniform. Typically only a minimum thickness is specified for the entire wall and applies to both the mastic supported on the gypsum board surfaces and the mastic supported only by the integrity of the material across the seams. The aging and deflection of the wall under dynamic wind loads on the building endanger the integrity of the moistureproof coating in the seam areas. It is believed that failure of the moistureproofing in the seam areas will be a cause of significant future problems in this type of construction.